Iran insists that its nuclear program is for peaceful purposes. But Tehran's declaration in late September of a second, previously undisclosed, uranium enrichment facility has heightened Western suspicions that it seeks weapons as well – and may have additional secret facilities. The US, Britain, France, Russia, China, and Germany met on Oct. 1 with Iran in Geneva for nuclear talks but reached no concrete results, though all parties agreed to meet again before the end of October.

Israel has in recent months repeatedly warned against indefinite talks, declaring Iran's nuclear ambitions to be the most urgent threat to the region. Though the effectiveness and wisdom of an Israeli strike are matters for debate, Israel has made clear it's a serious option.

When Dan Halutz, the former head of Israel's air force, was asked a few years ago to what lengths Israel would be willing to go to stop Iran's nuclear program, he famously said: "2,000 kilometers" – roughly the distance between Israel and Iran's main nuclear sites.

Can Israel stop Iran's nuclear program?

The consensus among experts is that an Israeli attack could slow Iran's nuclear progress for a few years, but would be unlikely to stop it. Why? Iran is prepared.

Israel's lightning strike that destroyed Iraq's Osirak nuclear reactor in 1981 is often spoken of as a model for potential Israeli action against Iran, along with a 2007 strike on an unguarded, unfinished nuclear plant in Syria.

The Iraqi and Syrian targets were single, above-ground sites. Attacking Iran is a much different proposition: It involves multiple sites and underground facilities, and would require Israeli jets to fly far longer distances and potentially face more advanced enemy weapons.

"It would be a very complex operation," says Brig. Gen. Shlomo Brom (ret.), former head of strategic planning for the Israeli military's general staff and now a senior researcher at the Institute for National Security Studies in Tel Aviv. "I don't think you can make the comparison to Osirak or Syria. In those cases it was one target ... and the ability of those two countries to do anything [against Israel] was nonexistent."

Iran has at least 17 widely dispersed nuclear sites in addition to the main facility at Natanz, built underground with at least some measures to withstand the "bunker buster" bombs in Israel's arsenal.

Brom says estimating the efficacy of an attack is difficult, but that it could probably slow Iran's nuclear program by about five years at most.

How would an attack be carried out?

Israel would probably use F-15 or F-16 fighter jets, which would have to fly 1,100 miles to reach Natanz and further for targets such as the nuclear reactor at Bushehr in the south. That distance is near the outer limit of such an aircraft's ability, though the planes can go longer distances by attaching additional fuel tanks or re-fueling in midair. The most direct routes go over Saudi Arabia, some via Iraq.

Though Saudi Arabia is unlikely to engage Israeli aircraft, and Iraq has no capabilities of its own, neither country is likely to officially approve such an attack and would be unlikely to participate in search and rescue efforts if an Israeli plane is damaged. An Israeli plane forced to land in either country would prove a diplomatic nightmare.

How might Iran respond?

The Iranians would undoubtedly try to shoot the planes down during their roughly 400-mile trip in its airspace. Iran has 29 Russian-built Tor-M1 mobile missile defense systems, which the country publicly unveiled at a military parade in late September, during which President Mahmoud Ahmadinejad vowed to cut the hands off any attacker. Iran recently tested missiles that, like previous versions, have the ability to reach Israel and US military bases in the region.

Other options for retaliation against Israel would be through Hezbollah, the movement Iran has helped arm and train that has the capacity to fire missiles and mortars at Israel from its base in southern Lebanon. Gerald Steinberg, a politics professor at Israel's Bar Ilan University who studies proliferation issues, says that while such retaliation is likely, it's something Israel would be willing to endure, since that threat is seen as far less than that of an Iranian nuclear weapon.

How likely is an attack?

The probability of an Israeli attack at the moment is very low. President Obama has opposed unilateral action by Israel, and Israeli officials appear willing to give the recently restarted nuclear dialogue with Iran at least until the end of the year. "If nothing happens in a few months and Iran is going full steam, [and] there's no greater monitoring, then I think the Israeli view will be, 'Let's go and look at our other options,' " says Professor Steinberg.

What would be the cost of a strike?

Brom says that the political costs for Israel of a unilateral attack could be huge, as could the consequences for the US.

"Iran has a very limited ability to strike out directly at Israel, but they have much more influence closer to home," he says, pointing out that retaliation against US troops in Iraq and Afghanistan would be probable. "They can affect the behavior of others in Iraq and Afghanistan and in the Arab Gulf states, and they can cause much harm to the export of oil from the Gulf, which hurts everybody.

For Israel's part, he says, because its relationship with the US is "of central strategic importance" that implies that Israeli leaders will "try to delay the decision as much as possible, and when it is impossible to delay anymore then it will still be a tough and difficult decision."

Steinberg agrees. "Even the more hawkish Israelis are very aware of the costs of a military operation, not just in terms of retaliation but in long-term Israeli-Iranian relations and in the stability of the region. Military action is the last and least desirable option."